Estrogen has long been implicated in the etiology of carcinogenesis and tumor growth as well as in its various normal metabolic effects on target tissues such as the uterus. To enhance our understanding of the mechanism of estrogen action in these different events, and knowing that the nuclear accumulation of estrogen is essential for estrogen action, we propose to examine the nuclear acceptor site for the estrogen- receptor complex. To avoid various artifacts and to reach an unequivocal resolution in the course of our studies, the proposed research covers experiments related to the following specifics: a) Formation of the estrogen-receptor-chromatin complex under physiological conditions. b) Fractionation of chromatin fragments containing the specific acceptor site on a specially prepared affinity column by a stereospecific exchange reaction. c) Selective elution of chromatin components from the column by a stereospecific exchange reaction. d) Biological characterization of the isolated acceptor molecule.